ML19312D863

Submits Addl Info Re Equation for Effect of Uncertainty in Dp/Dt at Min Critical Moderator Height for Accident Condition

ML19312D863
Person / Time
Site:	Lynchburg Research Center
Issue date:	04/30/1980
From:	Olsen A BABCOCK & WILCOX CO.
To:	Reid R Office of Nuclear Reactor Regulation
References
NUDOCS 8005050277
Download: ML19312D863 (3)

Text

i k{N 8005050 %,77' Babcock &Wilcox nesea,cn aoo oe eionment omision P.O. Box 1260, Lynchburg, Va. 24505 Telephone: (804) 384-5111 April 30, 1980 Mr. Robert W. Reid, Chief Operating Reactors Branch #4 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C. 20555 License: CX-10, docket 50-13 Reference 1 BAW-1484-7 " Critical Experiments Supporting Close Proximity Water Storage of Power Reactor Fuel" July 3 9/9 Reference 2 Letter to Mr. Robert W. Reid from A. F. Olsen, dated October 18, 1979, requesting license amendment Reference 3 Letter to Mr. Robert W. Reid from A. F. Olsen, dated April 11, 1980, providing additional information in support of amendment request

Dear Mr. Reid:

It has been brought to our attention by Mr. Harold Bernard and Ms. Jocelyn Mitchell of your staff, that we did not include in our analysis the effect of uncertainty in dp/dt at minimum critical moderator height for the accident condition.

H2 p= C/2 (H + A)4

("9""*I " 1)

Hi Equation 1 gives the reactivity addition which results when the moderator height of the core is raised from Hi to H .2C & A are curve fitting constants.

Reference 1 from which the values for C & A were taken, gives values of 3%,

1% and 6.7% respectively for (1) the uncertainty in p due to the uncertainty in in experimental measurements; (2) the uncertainty in p due to error in the least squares fit; and (3) the uncertainty in p due to uncertainty in the delayed neutron fraction. If all three of these uncertainties are combined in the most unfavorable manner, a total uncertainty of 10.7% results.

We have examined the effect of distributing the total uncertainty between the parameters A & C of equation 1 and have concluded that the largest re-activity addition rate results-for the loose packed square core when all of the The Babcock & Wilcox Company / Established 1867

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Mr. Robert W. Reid April 30, 1980 Page 2 uncertainty is due to an uncertainty in the parameter C. Since equation 1 shows p to be cirectly proportional to C, we have considered the case where C is uncertain by 10.7%.

The reactivity addition rate is calculated fr,m the equation:

6p AC g= (Ho + A)3 (equation 2) where:

n C/2 o = - A

1. ex + - 0.18 1 5 + A) p =

excess reactivity (% AK/K) obtained for full moderator height by KENO calculation.

=

A 0.0459 cm/sec =

maximum rate at which the moderator can rise with the loose packed square core loaded.

In our original application submittal (Reference 2), we made the calcu-lation of dp/dt using a value for p of 18.7% AK/K and a value for C of 61688 cm2 % AK/K. The value obtained for dp/dt was 0.047% AK/K/sec. If we reduce C by 10.7%, the value obtained for dp/dt is 0.049% AK/K/sec.

In our supplemental submittal (Reference 3), we made the calculation using a value for pex of 20.6% AK/K, and a value for C of 61688 cm2 % AK/K. (The value of p was' raised from its previous value of 18.7% AK/K to account for a possible 1.hk AK/K error in the results of the KENO calculation.) The value obtained for dp/dt was 0.054% AK/K/sec (which we rounded up to 0.055 in our supplemental submittal). If we reduce C by 10.7%, we obtain a value' for dp/dt of 0.056% AK/K/sec.

Being very conservative, we have examined the combined effect of (1) re-ducing C by'10.7%, (2) increasing p ex by 1.9% AK/K and (3) reducing the fuel

, temperature coefficient by 10%. Results from the point kinetics model of the maximum credible accident predict that the peak clad temperature would be l

l l

l L- - _

i

V Mr. Robert W. Reid April 30, 1980 Page 3 '

raisgd to 832" F. This is still considerably below the acceptable value of 1050 F given in amendment 5.

Thank you for your prompt consideration and if you require additional information, please contact me.

Yours very truly, BABCOCK & WILCOX COMPANY LYNCilBURG RESEARCll CENTER V

A. F. Olsen License Administrator nwt Attachment Subscribed and sworn to'before me this N NII day of 6 , 1980.

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Notary Public Hy commission expires [k-/C'[//Yf t